The present invention relates generally to paper or tissue products. More particularly, the invention concerns methods for applying adsorbable chemical additives to the fibers of pulps during the pulp processing and the paper products that can be obtained by the methods.
In the manufacture of paper products, it is often desirable to enhance physical and/or optical properties by the addition of chemical additives. Typically, chemicals such as softeners, colorants, brighteners, strength agents, etc. are added to the fiber slurry upstream of the headbox in a paper making machine during the manufacturing or converting stages of production to impart certain attributes to the finished product. These chemicals are usually mixed in a stock chest or stock line where the fiber slurry has a fiber consistency of from between about 0.15 to about 5 percent or spraying the wet or dry paper or tissue during production.
One disadvantage of adding a chemical at each paper machine is that the manufacturer has to install equipment on each paper machine to accomplish the chemical addition. This, in many cases, is a costly proposition. In addition, the uniformity of the finished product coming off of each paper machine may vary depending upon how the chemical was added, variations in chemical uniformity and concentrations, the exact point of chemical introduction, water chemistry differences among the paper machines as well as personnel and operational differences of each paper machine.
Another difficulty associated with wet end chemical addition is that the water soluble or water dispersible chemical additives are suspended in water and are not completely adsorbed onto the fibers prior to formation of the wet mat. To improve adsorption of wet end additives, chemical additives are often modified with functional groups to impart an electrical charge when in water. The electrokinetic attraction between charged additives and the anionically charged fiber surfaces aids in the deposition and retention of chemical additives onto the fibers. Nevertheless, the amount of chemical additive that can be retained in the paper machine wet end generally follows an adsorption curve exhibiting diminishing incremental adsorption with increasing concentration, similar to that described by Langmuir. As a result, the adsorption of water soluble or water dispersible chemical additives may be significantly less than 100 percent, particularly when trying to achieve high chemical additive loading levels.
Consequently, at any chemical addition level, and particularly at high addition levels, a fraction of the chemical additive is retained on the fiber surface. The remaining fraction of the chemical additive remains dissolved or dispersed in the suspending water phase. These unadsorbed chemical additives can cause a number of problems in the papermaking process. The exact nature of the chemical additive will determine the specific problems that may arise, but a partial list of problems that may result from unadsorbed chemical additives includes: foam, deposits, contamination of other fiber streams, poor fiber retention on the machine, compromised chemical layer purity in multi-layer products, dissolved solids build-up in the water system, interactions with other process chemicals, felt or fabric plugging, excessive adhesion or release on dryer surfaces, physical property variability in the finished product.
Therefore, what is lacking and needed in the art is a method for applying adsorbable chemical additives onto pulp fiber surfaces in the initial or primary pulp processing, providing more uniform chemical additions to the pulp fiber and a reduction or elimination of unadsorbed chemical additives in the process water on a paper machine. The method minimizes the associated manufacturing and finished product quality problems that would otherwise occur with conventional wet end chemical addition at the paper machine.
It has now been discovered that adsorbable chemical additives can be adsorbed onto pulp fibers that have never been dried at high and/or uniform levels with at most a minimal amount of unadsorbed chemical additives present in the papermaking process water after the treated pulp fiber has been redispersed in water. This is accomplished by treating a fiber slurry comprising pulp fiber and water with an excess of the adsorbable chemical additive, allowing sufficient residence time for adsorption to occur, and filtering or otherwise dewatering the fiber slurry to remove water and unadsorbed chemical additives.
Hence in one aspect, the invention resides in a method for applying adsorbable chemical additives to the pulp fibers. The method comprises creating a fiber slurry comprising water, pulp fibers that have never been dried, and an adsorbable chemical additive. The fiber slurry having the chemical additive may be formed into a wet fibrous web using a web forming apparatus. The wet fibrous web is dried to a predetermined consistency. In other embodiments of the present invention, the process may include further dewatering thereby forming a crumb-form. The dried fibrous web may have retained from between about 10 to about 100 percent of the adsorbable chemical additive.
According to another embodiment of the present invention is a method for adding an adsorbable chemical to the pulp fiber during the pulp processing prior to the drying stage. During the pulp processing, upstream of a paper machine, one can obtain chemically treated pulp fiber that is essentially homogeneous in chemical adsorption. Furthermore, the chemically treated pulp fiber can be transported to several different paper machines that may be located at various sites, and the quality of the finished product from each paper machine will be more consistent. Also, by chemically treating the pulp fiber before the pulp fiber is available for use on multiple paper machines or multiple runs on a paper machine, the need to install equipment at each paper machine for the adsorbable chemical addition can be eliminated.
This method for processing pulp fibers also enables higher and more uniform concentrations of adsorbable chemical additives to be adsorbed by the pulp fibers while at the same time maintaining significantly lower levels of unadsorbed chemical additive in the water phase of a papermaking machine compared to paper machine wet end chemical additions.
The term xe2x80x9cadsorbablexe2x80x9d is used herein to refer to a chemical additive that can be assimilated by the surface of a pulp fiber, in the absence of any chemical reaction involving the chemical additive and the fiber. Once the chemical additive is adsorbed, it may or may not be absorbed into the pulp fiber. The term xe2x80x9cunadsorbedxe2x80x9d refers to any portion of the adsorbable chemical additive that is not adsorbed by the pulp fiber and thus remains suspended in the process water. The term xe2x80x9cweb-forming apparatusxe2x80x9d includes fourdrinier former, twin wire former, cylinder machine, press former, crescent former, and the like known to those skilled in the art.
The consistency of the fiber slurry is from about 0.5 to about 15 percent. In other embodiments, the consistency of the fiber slurry is from about 2 to about 10 percent or from about 3 to about 5 percent. The consistency of the dried fibrous web is from about 45 to about 100 percent. In other embodiments, the consistency of the dried fibrous web is from about 60 to about 100 percent or from about 85 to about 95 percent. The consistency of the wet fibrous web is from about 30 to about 45 percent. In other embodiments, the consistency of the wet fibrous web is from about 35 to about 45 percent or from about 40 to about 45 percent. The consistency of the crumb form is from about 50 to about 85 percent. In other embodiments, the consistency of the crumb form is from about 60 to about 85 percent or from about 80 to about 85 percent.
The present method allows for the production of pulp fibers that are useful for making paper products. This results in a pulp fiber, which after drying, has different mechanical properties than if the chemical treatment is carried out on pulp fiber in the once dried state. One aspect of the present invention is a more uniformly chemically treated pulp fiber, replacing the need for costly and variable chemical treatments at one or more paper machines. Another aspect of the invention resides in a pulp fiber that has a higher chemical additive loading than could otherwise be achieved in combination with no or a relatively low level of unadsorbed chemical additive in the process water on a paper machine. This is because chemical additive loading via wet end addition is often limited by the level of unadsorbed chemical and/or contact time, as well as its associated processing difficulties such as foam, deposits, chemical interactions, felt plugging, excessive dryer adhesion or release or a variety of paper physical property control issues caused by the presence of unadsorbed chemical in the process water on the paper machines.
In another embodiment, a fiber slurry of the present invention comprises water, pulp fibers having an adsorbable chemical additive adsorbed onto the fiber surface. The amount of chemical additive adsorbed onto the pulp fibers is about 0.1 kilogram per metric ton or greater, and the amount of unadsorbed chemical additive in the water is between 0 and about 90 percent of the amount of adsorbable chemical additive added to the pulp fibers. In particularly desirable embodiments, the amount of adsorbed chemical additive is about 0.5 kg/metric ton or greater, particularly about 1 kg/metric ton or greater, and more particularly about 2 kg/metric ton or greater. Once the wet or dried fibrous wet is redispersed at the paper machine, the amount of unadsorbed chemical additive in the water phase is between 0 and about 15 percent, particularly between 0 and about 10 percent, and more particularly between 0 and about 7 percent, of the amount of adsorbed chemical additive.
According to one embodiment of the present invention, the method for adding an adsorbable chemical additive to pulp fiber comprises creating a fiber slurry. The fiber slurry comprises water, pulp fibers that have never been dried, and an adsorbable chemical additive The fiber slurry having the adsorbable chemical additive is passed to a web-forming apparatus where a wet fibrous web is formed from the fiber slurry. The wet fibrous web is dried to a predetermined consistency. The resulting dried fibrous web may have from between about 10 to about 100 percent retention of the adsorbable chemical additive on the fibers. The dried fibrous web may be transported to a paper machine. The dried fibrous web is mixed with water to form a wet slurry. The wet slurry contains the fibers having the adsorbable chemical additive secured thereto. A finished product having enhanced quality due to the retention of the adsorbable chemical additive on the fibers may be produced from the wet slurry.
Another aspect of the present invention resides in a method for making chemically treated paper products. The method comprising mixing pulp fibers that have never been dried with water to form a fiber slurry. An adsorbable chemical additive is added to the fiber slurry. The fiber slurry, containing the adsorbable chemical additive is formed into a wet fibrous web. This may be accomplished in a web-forming apparatus. The wet fibrous web may be dried to a predetermined consistency. The resulting dried fibrous web may have from about 10 to about 100 percent retention of the chemical additive. The pulp fibers, as a dried fibrous web, may be transported or otherwise delivered to one or more paper machines. The pulp fiber, as a dried fibrous web, is mixed with water to form a wet slurry. The wet slurry contains the pulp fibers having the adsorbable chemical additive secured thereto. A finished product having enhanced qualities due to the retention of the adsorbable chemical additive on the fibers may be produced.
Another aspect of the present invention resides in a method for making chemically treated finished paper or tissue products. The method comprising mixing pulp fibers that have never been dried with water to form a fiber slurry. An adsorbable chemical additive is added to the fiber slurry. The fiber slurry, containing the adsorbable chemical additive is formed into a wet fibrous web. This may be accomplished in a web-forming apparatus. The wet fibrous web may be dewatered to a predetermined consistency. In other embodiments, the pulp fiber may be processed to a wet lap or processed to a crumb form. The resulting pulp fiber may have from about 10 to about 100 percent retention of the adsorbable chemical additive. The pulp fibers, once treated with the adsorbable chemical additive, may be transported or otherwise delivered to one or more paper machines in the form of a wet fibrous web, a dried fibrous web, a wet lap, or a crumb form. The pulp fiber, as a wet fibrous web, a wet lap, or a crumb form, is mixed with water to form a wet slurry. The wet slurry contains the pulp fibers having the adsorbable chemical additive secured thereto. A finished product having enhanced qualities due to the retention of the adsorbable chemical additive on the fibers is produced.
Another aspect of the present invention resides in a method for making chemically treated paper products. The method comprises creating a fiber slurry comprising water, pulp fibers that have never been dried, and a first adsorbable chemical additive. At least a second adsorbable chemical additive may be added to the fiber slurry, thereby forming a multi-treated fiber slurry. The additional adsorbable chemical additives may be added simultaneously with the first adsorbable chemical additives or at different times or points of the pulp processing. The additional adsorbable chemical additives may be added simultaneously or at different times or points of the pulp processing. The multi-treated fiber slurry, containing the adsorbable chemical additives, is formed into a wet fibrous web. This may be accomplished in a web-forming apparatus. The wet fibrous web may be dried to a predetermined consistency. The resulting dried fibrous web may have from about 10 to about 100 percent retention of the adsorbable chemical additives. The pulp fibers, as a multi-treated dried fibrous web, is transported or otherwise delivered to one or more paper machines. The pulp fiber, as a multi-treated dried fibrous web, is mixed with water to form a wet slurry. The wet slurry contains the pulp fibers having the adsorbable chemical additives secured thereto. A finished product having enhanced qualities due to the retention of the adsorbable chemical additives on the fibers may be produced.
In other aspects of the present invention reside a method for making chemically treated paper products. The method comprises creating a fiber slurry comprising water, pulp fibers that have never been dried, and a first adsorbable chemical additive. At least a second adsorbable chemical additive may be added to the fiber slurry, thereby forming a multi-treated fiber slurry. The second or additional adsorbable chemical additives may be added simultaneously with the first adsorbable chemical additive or at different times or points of the pulp processing. The additional adsorbable chemical additives may be added simultaneously or at different times or points of the pulp processing. The multi-treated fiber slurry, containing the adsorbable chemical additives, is formed into a wet fibrous web. This may be accomplished in a web-forming apparatus. The wet fibrous web may be dried to a predetermined consistency. In other embodiments, the pulp fiber may be processed to a wet lap or processed to a crumb form. The resulting pulp fiber may have from about 10 to about 100 percent retention of the adsorbable chemical additives. The pulp fibers, once treated with the adsorbable chemical additives, may be transported or otherwise delivered to one or more paper machines in the form of a wet fibrous web, a wet lap, or a crumb form. The pulp fiber, as a multi-treated wet fibrous web, a wet lap, or a crumb form, is mixed with water to form a wet slurry. The wet slurry contains the pulp fibers having the adsorbable chemical additives secured thereto. A finished product having enhanced qualities due to the retention of the adsorbable chemical additives on the fibers may be produced.
The present invention is particularly useful for adding adsorbable chemical additives such as softening agents to the pulp fibers, allowing for the less problematic and lower cost production of finished products having enhanced qualities provided by the retained adsorbable chemical additives.
Hence, another aspect of the present invention resides in paper products formed from pulp fibers that have been chemically treated prior to a drying phase to minimize the amount of residual, unadsorbed chemical additives in the process water on a paper machine. The term xe2x80x9cpaperxe2x80x9d is used herein to broadly include writing, printing, wrapping, sanitary, and industrial papers, newsprint, linerboard, tissue, bath tissue, facial tissue, napkins, wipers, wet wipes, towels, absorbent pads, intake webs in absorbent articles such as diapers, bed pads, meat and poultry pads, feminine care pads, and the like made in accordance with any conventional process for the production of such products. With regard to the use of the term xe2x80x9cpaperxe2x80x9d as used herein includes any web containing cellulosic fibers alone or in combination with other fibers, natural or synthetic. It can be layered or unlayered, creped or uncreped, and can consist of a single ply or multiple plies. In addition, the paper or tissue web can contain reinforcing fibers for integrity and strength.
The adsorbable chemical additives that can be used in conjunction with the present invention include: dry strength aids, wet strength aids, softening agents, adsorbency aids, sizing agents, dyes, optical brighteners, chemical tracers, opacifiers, dryer adhesive chemicals, and the like. Additional forms of adsorbable chemical additives may include: pigments, emollients, humectants, viricides, bactericides, buffers, waxes, fluoropolymers, odor control materials and deodorants, zeolites, perfumes, vegetable and mineral oils, humectants, sizing agents, surfactants, moisturizers, UV blockers, antibiotic agents, lotions, fungicides, preservatives, aloe-vera extract, vitamin E, or the like. Suitable adsorbable chemical additives are adsorbable by the papermaking fibers and are water soluble or water dispersible.
The term xe2x80x9csoftening agentxe2x80x9d refers to any adsorbable chemical additive that can be incorporated into paper products such as tissue to provide improved tactile feel and reduce paper stiffness. A softening agent may be selected from the group consisting of quaternary ammonium compounds, quaternized protein compounds, phospholipids, silicone quaternaries, quaternized, hydrolyzed wheat protein/dimethicone phosphocopolyol copolymer, organoreactive polysiloxanes, and silicone glycols. These adsorbable chemical additives can also act to reduce paper stiffness or can act solely to improve the surface characteristics of tissue, such as by reducing the coefficient of friction between the tissue surface and the hand.
The term xe2x80x9cdyexe2x80x9d refers to any adsorbable chemical that can be incorporated into paper products, such as bathroom tissue, facial tissue, paper towels, and napkins, to impart a color. Depending on the nature of the adsorbable chemical, dyes may be classified as acid dyes, basic dyes, direct dyes, cellulose reactive dyes, or pigments. All classifications are suitable for use in conjunction with the present invention.
The term xe2x80x9cwater solublexe2x80x9d refers to solids or liquids that will form a solution in water, and the term xe2x80x9cwater dispersiblexe2x80x9d refers to solids or liquids of colloidal size or larger that can be dispersed into an aqueous medium.
The method for applying adsorbable chemical additives to the pulp fibers may be used in a wide variety of pulp finishing processing, including dry lap pulp, wet lap pulp, crumb pulp, and flash dried pulp operations. By way of illustration, various pulp finishing processes (also referred to as pulp processing) are disclosed in Pulp and Paper Manufacture: The Pulping of Wood, 2nd Ed., Volume 1, Chapter 12. Ronald G. MacDonald, editor, which is incorporated by reference.
In addition, in situations where more than one adsorbable chemical additive is to be employed, the adsorbable chemical additives may be added to the fiber slurry in sequence to reduce interactions between the adsorbable chemical additives. In other situations, the adsorbable chemical additives may be removed from the fiber slurry after another adsorbable chemical additive has been added to facilitate the removal process.
Many fiber types may be used for the present invention including hardwood or softwoods, straw, flax, milkweed seed floss fibers, abaca, hemp, kenaf, bagasse, cotton, reed, and the like. All known papermaking fibers may be used, including bleached and unbleached fibers, fibers of natural origin (including wood fiber and other cellulose fibers, cellulose derivatives, and chemically stiffened or crosslinked fibers), some component portion of synthetic fiber (synthetic papermaking fibers include certain forms of fibers made from polypropylene, acrylic, aramids, acetates, and the like), virgin and recovered or recycled fibers, hardwood and softwood, and fibers that have been mechanically pulped (e.g., groundwood), chemically pulped (including but not limited to the kraft and sulfite pulp processings), thermomechanically pulped, chemithermomechanically pulped, and the like. Mixtures of any subset of the above mentioned or related fiber classes may be used. The pulp fibers can be prepared in a multiplicity of ways known to be advantageous in the art. Useful methods of preparing fibers include dispersion to impart curl and improved drying properties, such as disclosed in U.S. Pat. No. 5,348,620 issued Sep. 20, 1994 and U.S Pat. No. 5,501,768 issued Mar. 26, 1996, both to M. A. Hermans et al. and U.S. Pat. No. 5,656,132 issued Aug. 12, 1997 to Farrington, Jr. et al.
According to the present invention, the adsorbable chemical treatment of the pulp fibers occurs prior to the drying phase of the pulp processing. The two generally accepted methods of drying include flash drying and can drying. Flash drying is most common with bleached, chemi-thermo-mechanical pulp (BCTMP). The present invention may also be applied to wet lap pulp processes without the use of can or flash dryers.
Numerous features and advantages of the present invention will appear from the following description. In the description, reference is made to the accompanying drawings which illustrate preferred embodiments of the invention. Such embodiments do not represent the full scope of the invention. Reference should therefore be made to the claims herein for interpreting the full scope of the invention.